This invention relates to the field of dopamine receptor partial agonists, and in particular to novel 4-piperazinyl-isatins, their preparation, and their therapeutic use, e.g., in the treatment of psychosis.
Dopamine antagonists have been used for years in the treatment of disorders of the dopaminergic system, such as schizophrenia. These antagonists block the D2 receptors. Unfortunately, this causes undesirable side effects. Dopamine autoreceptor agonists, including partial agonists, can be used to induce antipsychotic activity without causing the same side effects as antagonists.
Intrinsic activity at the dopamine D2 receptor may be predicted using the ratio of the xe2x80x9clow-affinity agonistxe2x80x9d (LowAg) state of the receptor and the xe2x80x9chigh-affinity agonistxe2x80x9d (HighAg) state of the receptor, i.e. LowAg/HighAg. These ratios correlate with the agonist, partial agonist, and antagonist activities of a given compound, and these activities characterize a compound""s ability to elicit an antipsychotic effect.
WO 94 13659 discloses fused benzo compounds of the general Formula I 
wherein X is selected from a broad base of divalent 3-4 membered groups, including the possibility of forming imidazoles, which potently bind to the 5-HT1A receptor and have central serotonergic 5HT1A activity for the treatment of certain psychic and neurological disorders.
EP 0138280 discloses piperazinyl compounds of Formula II having a bicyclic heteroaryl radical in the 4-position and a heteroaryl-, aryl-, or alkyl substituted carbamoylethyl or carbamoylpropyl in the 1-position. These compounds are alleged to show blood pressure lowering effect through a central mechanism. When n=1, the compounds are piperazines. 
WO 94 15919 (Formula III) and WO 94 21610 (Formula IV) disclose piperazine derivatives which act on the central nervous system by binding to 5-HT receptors, particularly 5-HT1A type, for the use in the treatment of CNS disorders, such as anxiety, depression, and cognition disorders. In both Formula III and Formula IV, Z and R1 refer to heteroaryl groups. 
R. E. Mewshaw et al (Bloorg. and Med. Chem. Leff. 8, 2675-2680, 1998) describe heteroarylpiperazines of Formula V which have excellent affinity for the D2 receptor, and are potentially useful as antipsychotic agents. 
E. Giovannini et al. (Helv. Chim. Acta 40, 249, 1957) reported that 4-amino-isatin had been prepared.
Several techniques useful for forming derivatives are known in the art. G. Friedmann et al. (J. Org. Chem. 44, 237, 1979) described lithiation of N,N,Nxe2x80x2,Nxe2x80x2-tertramethyl-ortho- and para-phenylenediamine. An improvement was revealed by W. Fuhrer and H. W. Gschwend (J. Org. Chem. 44, 1133, 1979) which involved a combined ortho-directing effect as illustrated by lithiation of N-pivaloyl-3-methoxyaniline. P. Hewawasam and N. A. Meanwell (Tetrahedron Letters, 3, 7303, 1994) disclosed the conversion of several 3-(suitably substituted) anilines into corresponding 2-(xcex1-ketoesters) by means of diethyl oxalate; subsequent hydrolytic deprotection produced substituted isatins. However, the literature does not disclose the analogous lithiation of metaphenylenediamine derivatives, such as 3-(4xe2x80x2-R-piperazin-1xe2x80x2-yl)anilines. The choice of the directing and protecting groups appears to be of critical importance in lithiating different species, and such choice is by no means obvious, as is indicated by the disclosures of P. Hewawasam and N. A. Meanwell (Tetrahedron Letters, 35, 7303, 1994) and V. Snieckus, Lect. Heterocylic Chem., 95-106, 1984).
The present invention comprises novel 4-piperazinyl compounds of Formula VI 
wherein
Y is hydrogen, methyl, methoxy, methylthio, or trifluoromethyl;
R is H, C1-3alkyl, or (CH2)nAr;
n is 0, 1, or 2; and
Ar is phenyl or methoxyphenyl,
and pharmaceutically acceptable salts thereof.
The present invention further comprises compounds of Formula VII and Formula VIII 
which are useful in making compounds of Formula VI, wherein Y and R have the same definition as in Formula VI. Ph represents a phenyl group and Et represents an ethyl group.
The present invention also includes compositions containing Formula VI compounds; methods for making compounds of Formula VI and Formula VII; and methods of treatment comprising administering a compound of Formula VI or a pharmaceutically acceptable salt thereof to a mammal to reduce dopamine synthesis, and/or to treat disorders of the dopaminergic system, such as schizophrenia, Parkinson""s disease, hyperprolactinemia, depression, and Tourette""s syndrome. Preferably, the compounds of the invention are those wherein Rxe2x80x2 is a hydrogen atom and R is not a hydrogen atom; such compounds wherein Ar is phenyl, n is 1, and Y is hydrogen are more preferred.
This invention comprises novel isatins substituted in position 4 with a tertiary amino group, preferably 4-(4xe2x80x2-R-piperazin-1xe2x80x2-yl)isatins, where R is H, alkyl, or aralkyl. One highly preferred embodiment of the invention is 4-(4xe2x80x2-benzylpiperazin-1xe2x80x2-yl)isatin.
The 4-piperazinylisatins of this invention have biological activity as an antipsychotic agent. These compounds are essentially free from extrapyramidal side effects (EPS). The compounds of this invention are selective autoreceptor agonists, functioning primarily to activate only autoreceptors versus postsynaptic D2 dopamine receptors. As such, they provide functional modulation of dopamine systems of the brain without the excessive blockade of the postsynaptic dopamine receptors, which have been observed to be responsible for the serious side effects frequently exhibited by agents found otherwise clinically effective for treatment of schizophrenia. Activation of the dopamine autoreceptors results in reduced neuronal firing as well as inhibition of dopamine synthesis and release and therefore provide a means of controlling hyperactivity of the dopaminergic systems.
More specifically, the compounds of this invention comprise those depicted by the following Formula VI: 
wherein
Y is hydrogen, methyl, methoxy, methylthio, or trifluoromethyl;
R is H, C1-3alkyl, or (CH2)nAr;
n is 0, 1, or 2; and
Ar is phenyl or methoxyphenyl,
and pharmaceutically acceptable salts thereof.
Those skilled in the art will be readily able to determine which salts of the compounds of this invention are pharmaceutically acceptable. The pharmaceutically acceptable salts of the compounds of this invention include those derived from such organic and inorganic acids, such as: acetic, lactic, citric, fumaric, tartaric, succinic, maleic, malonic, oxalic, hydrochloric, hydrobromic, phosphoric, nitric, sulfuric, methanesulfonic, methylbenzene sulfonic, and similarly known acceptable acids.
The term alkyl as used herein includes both straight chain and branched moieties.
A preferred embodiment of this invention is compounds of formula VI wherein Y is hydrogen, methyl, methoxy at the 5 or 7 position, methylthio at the 7 position, or trifluoromethyl at the 5 or 6 position, and R is (CH2)Ar. Highly preferred compounds of this invention include those compounds of Formula VI in which Y=H, n=1 and Ar=phenyl.
The compounds of this invention can be prepared from starting materials that are either commercially available or can be prepared by standard procedures known to those skilled in the art. The compounds of Formula VI can be generally prepared as shown in Reaction Scheme I, which specifically illustrates the reaction scheme for making 4-(4-benzyl-piperazin-1-yl)-1H-indole-2.3-dione. 
Compound 7 may be useful in the preparation of more substituted isatins, for example by substitution on the isatin nitrogen, or removal of the piperazinyl benzyl group and subsequent substitution with alkyl or aralkyl groups.
Other compounds of this invention wherein Y is not H may be prepared in a manner analogous to Reaction Scheme I. Illustrative examples of these compounds are presented in the table below, which shows the derivatives of compound 7 that will be formed according to Reaction Scheme 1 starting with a specified compound 1:
Other examples will be readily apparent to those skilled in the art.
The present invention discloses a useful approach to derivatives of 4-amino-isatins and, as specifically defined in Reaction Scheme I, to 4-(4xe2x80x2-benzylpiperazin-1-yl)isatin. The synthetic methodology involves regiospecific, ortho-directed lithiation of N-[3-(4xe2x80x2-benzylpiperazin-1xe2x80x2-yl)phenyl]-2,2-dimethylpropionamide (i.e., pivaloylamide), followed by treatment of the metalated species with diethyl oxalate, and ring closure. The choice of directing and protecting groups appears to be of critical importance in lithiating different species.
The starting material of the present invention, 1-(3-nitrophenyl)-4-benzylpiperazine, is prepared by condensation of benzylpiperazine with 1-fluoro-3-nitrobenzene in the same fashion as described by H. Kotsuki et al (Synthesis, 12, 1147-1148, 1990), and R. Paul et al. (J. Med. Chem. 36, 2716, 1993) for 1-(3-nitrophenyl)-4-methylpiperazine. The 1-(3-aminophenyl)-4-benzyl-piperazines are novel compounds, useful pharmaceutical intermediates, and potential precursors of other piperazine derivatives.
The compounds of this invention may be administered orally or parenterally, neat or in combination with conventional pharmaceutical carriers. Applicable solid carriers for pharmaceutical compositions containing the compounds of this invention can include one or more substances which may also act as flavoring agents, lubricants, solubilizers, suspending agents, fillers, glidants, compression aids, binders or tablet-disintegrating agents or an encapsulating material. In powders, the carrier is a finely divided solid which is in admixture with the finely divided active ingredient. In tablets, the active ingredient is typically mixed with a carrier having the necessary compression properties in suitable proportions and compacted in the shape and size desired. The powders and tablets preferably contain up to 99% of the active ingredient. Suitable solid carriers include, for example, calcium phosphate, magnesium stearate, talc, sugars, lactose, dextrin, starch, gelatin, cellulose, methyl cellulose, sodium carboxymethyl cellulose, polyvinyl-pyrrolidone, low melting waxes and ion exchange resins.
Liquid carriers may be used in preparing solutions, suspensions, emulsions, syrups and elixirs containing one or more compounds of the present invention as active ingredient(s). The active ingredient can be dissolved or suspended in a pharmaceutically acceptable liquid carrier such as water, an organic solvent, pharmaceutically acceptable oils or fat, or mixtures of any of these carriers.
The liquid carrier can contain other suitable pharmaceutical additives such as solubilizers, emulsifiers, buffers, preservatives, sweeteners, flavoring agents, suspending agents, thickening agents, coloring agents, viscosity regulators, stabilizers or osmo-regulators. Suitable examples of liquid carriers for oral and parenteral administration include water (particularly containing additives, e.g., cellulose derivatives, preferably sodium carboxymethyl cellulose solution), alcohols (including monohydric alcohols and polyhydric alcohols, e.g., glycols) and their derivatives, and oils (e.g., fractionated coconut oil, or arachis oil). For parenteral administration the carrier can also be an oily ester such as ethyl oleate and isopropyl myristate. Sterile liquid camrers are needed for use in sterile liquid compositions for parenteral administration.
Liquid pharmaceutical compositions which are essentially sterile solutions or suspensions can be utilized by, for example, intramuscular, intraperitoneal or subcutaneous injection. Sterile solutions can also be administered intravenously. Oral administration may accomplished using either liquid or solid composition forms.
Preferably the pharmaceutical composition is in unit dosage form, e.g. as tablets or capsules, in which each unit dose contains an appropriate quantity of the active ingredient. The unit dosage forms of compositions according to the present invention can be packaged in any manner acceptable in the art; for example, these compositions may be packaged in packets containing solid forms such as powder, or in vials, ampoules, prefilled syringes or sachets containing liquids. The unit dosage form can be, for example, a capsule or tablet itself, or it can be the appropriate number of any such compositions in package form.
The dosage to be used in the treatment of a specific psychosis must be subjectively determined by the attending physician. The variables involved include the specific psychosis and the size, age and response pattern of the patient. The treatment of substance abuse follows the same method of subjective drug administration under the guidance of the attending physician. Based upon the potency of the compounds of this invention, it is believed that the appropriate dose for a human patient will be from about 5 to about 100 mg/day. Conventionally, such treatments begin with the lower dose with gradual increase at the rate of about 5 mg/day until the desired response pattern is achieved. The optimum human dosage typically is expected to be in the range of about 15 mg/day to about 75 mg/day.
The following Examples illustrate specific embodiments of this invention; however, the scope of this invention is not limited to the embodiments illustrated in these Examples, but encompasses the full scope of the subject matter set forth in the appended claims.